SDL_OpenAudio(3) SDL API Reference SDL_OpenAudio(3)NAME
SDL_OpenAudio- Opens the audio device with the desired
parameters.
SYNOPSIS
#include "SDL.h"
int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec
*obtained);
DESCRIPTION
This function opens the audio device with the desired
parameters, and returns 0 if successful, placing the
actual hardware parameters in the structure pointed to by
obtained. If obtained is NULL, the audio data passed to
the callback function will be guaranteed to be in the
requested format, and will be automatically converted to
the hardware audio format if necessary. This function
returns -1 if it failed to open the audio device, or
couldn't set up the audio thread.
To open the audio device a desired SDL_AudioSpec must be
created.
SDL_AudioSpec *desired;
.
.
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
You must then fill this structure with your desired audio
specifications.
desired->freq
desired->format
desired->samples
desired->callback
void callback(void *userdata, Uint8 *stream, int len);
userdata is the pointer stored in userdata field of the
SDL_AudioSpec. stream is a pointer to the audio buffer you
want to fill with information and len is the length of the
audio buffer in bytes.
desired->userdata
SDL_OpenAudio reads these fields from the desired
SDL_AudioSpec structure pass to the function and attempts
to find an audio configuration matching your desired. As
mentioned above, if the obtained parameter is NULL then
SDL with convert from your desired audio settings to the
hardware settings as it plays.
If obtained is NULL then the desired SDL_AudioSpec is your
working specification, otherwise the obtained
SDL_AudioSpec becomes the working specification and the
desirec specification can be deleted. The data in the
working specification is used when building SDL_AudioCVT's
for converting loaded data to the hardware format.
SDL_OpenAudio calculates the size and silence fields for
both the desired and obtained specifications. The size
field stores the total size of the audio buffer in bytes,
while the silence stores the value used to represent
silence in the audio buffer
The audio device starts out playing silence when it's
opened, and should be enabled for playing by calling
SDL_PauseAudio(0) when you are ready for your audio call-
back function to be called. Since the audio driver may
modify the requested size of the audio buffer, you should
allocate any local mixing buffers after you open the audio
device.
EXAMPLES
/* Prototype of our callback function */
void my_audio_callback(void *userdata, Uint8 *stream, int len);
/* Open the audio device */
SDL_AudioSpec *desired, *obtained;
SDL_AudioSpec *hardware_spec;
/* Allocate a desired SDL_AudioSpec */
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
/* Allocate space for the obtained SDL_AudioSpec */
obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
/* 22050Hz - FM Radio quality */
desired->freq=22050;
/* 16-bit signed audio */
desired->format=AUDIO_S16LSB;
/* Mono */
desired->channels=0;
/* Large audio buffer reduces risk of dropouts but increases response time */
desired->samples=8192;
/* Our callback function */
desired->callback=my_audio_callback;
desired->userdata=NULL;
/* Open the audio device */
if ( SDL_OpenAudio(desired, obtained) < 0 ){
fprintf(stderr, "Couldn't open audio: %s
", SDL_GetError());
exit(-1);
}
/* desired spec is no longer needed */
free(desired);
hardware_spec=obtained;
.
.
/* Prepare callback for playing */
.
.
.
/* Start playing */
SDL_PauseAudio(0);
SEE ALSO
SDL_AudioSpec, SDL_LockAudio, SDL_UnlockAudio, SDL_Pause-
Audio
SDL Tue 11 Sep 2001, 22:58 SDL_OpenAudio(3)
